The present invention relates to a method for producing thin film transistors (hereinafter referred to as TFT) that comprise a crystalline silicon film.
Known are TFT comprising an amorphous silicon film. Such conventional TFT are used essentially for constructing active-matrix circuits to be in active-matrix type, liquid crystal display devices.
However, amorphous silicon TFT are problematic in that their acting speed is low and that they could not be used in practicable P-channel devices.
Because of such their problems, amorphous silicon TFT are used almost nowhere except for active-matrix circuits.
As one means capable of solving the problems, known is a structure comprising a crystalline silicon film.
To obtain such a crystalline silicon film, a heating method is known at present, in which, however, films of good quality could not be obtained.
The present applicant has already developed a technique of obtaining a crystalline silicon film under heat, in which the crystallization of silicon under heat is promoted by a predetermined metal element.
Concretely, the method developed by the applicant comprises introducing a metal element such as typically nickel into an amorphous silicon film followed by heating the film to thereby convert it into a crystalline silicon film.
The crystallinity of the crystalline silicon film as obtained in that method is higher than that of the others as obtained by heating only.
However, in the method, the nickel element used remains in the crystalline silicon film formed, thereby having some negative influences on the characteristics of TFT comprising the film.
Concretely, one problem with TFT comprising the film is that the characteristics of TFT vary with the lapse of time to lower the reliability thereof.
Another problem is that the method requires the nickel addition and therefore the steps constituting the method are complicated.
The invention disclosed herein is to provide a technique of improving TFT having a crystalline silicon film to be formed by the use of a metal element capable of promoting the crystallization of silicon, and is characterized in that the metal element used is prevented from having some negative influences on the characteristics of the TFT. The invention is further characterized in that the steps constituting the method of the invention are simplified as much as possible.
One aspect of the invention disclosed herein is a method for producing a semiconductor device, which comprises diffusing a metal element capable of promoting the crystallization of silicon, from a partial region of an amorphous silicon film into the film, followed by making the metal element gettered by a gettering element, and is characterized in that;
The metal element and the gettering element are introduced into the silicon film from a material as provided to be in contact with said partial region of the film.
Most preferably, the metal element capable of promoting the crystallization of silicon is Ni, and the gettering element is phosphorus. This combination produces the best results of crystallization of silicon with Ni and removal of Ni with phosphorus.
In general, as the element capable of promoting the crystallization of silicon, employable are one or more kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au, Ge, Pd and In.
As the gettering element, usable is arsenic or antimony except phosphorus. The gettering element referred to herein is one that getters the metal element having been used herein for promoting the crystallization of silicon.
Preferably, the metal element is introduced into the silicon film under heat at a temperature falling between 500xc2x0 C., and 750xc2x0 C., and the gettering element is introduced thereinto under heat at a temperature falling between 800xc2x0 C. and 1100xc2x0 C.
This heating mode is based on the fact that the metal element is diffused under heat within such a temperature range falling between 500xc2x0 C. and 750xc2x0 C. to promote the crystallization of silicon, while the gettering element is diffused little within the temperature range. Specifically, in the method of the invention, the amorphous silicon film is selectively crystallized under heat at a temperature falling between 500xc2x0 C. and 750xc2x0 C., and thereafter it is further heated at a temperature falling between 800xc2x0 C. and 1100xc2x0 C., at which the gettering element can diffuse, whereby the gettering element is diffused into the film to getter the metal element.
In this method of the invention, the source of the metal element for promoting the crystallization of silicon and the source of the gettering element may be in one and the same material, whereby the method is simplified.
In place of the amorphous silicon film, employable is an amorphous film consisting essentially of silicon. For example, employable is an amorphous, compound semiconductor film, of which 50% or more is silicon.
Another aspect of the invention is a method for producing a semiconductor device, which comprises;
a step of keeping a material that contains phosphorus and a metal element capable of promoting the crystallization of silicon, in contact with a partial region of an amorphous silicon film,
a step of first heat treatment for diffusing the metal element from said partial region into the amorphous silicon film to thereby attain crystal growth in the film, and
a step of second heat treatment for diffusing phosphorus from said partial region into the amorphous silicon film to thereby make the metal element gettered by the thus-diffused phosphorus,
wherein;
the diffusion distance for the metal element is longer than that for phosphorus.
Still another aspect of the invention is a method for producing a semiconductor device, which comprises;
a step of keeping a material that contains phosphorus and a metal element capable of promoting the crystallization of silicon, in contact with a partial region of an amorphous silicon film,
a step of first heat treatment for diffusing the metal element from said partial region into the amorphous silicon film to thereby attain crystal growth in the film, and
a step of second heat treatment for diffusing phosphorus from said partial region into the amorphous silicon film to thereby make the metal element gettered by the thus-diffused phosphorus,
wherein;
the temperature for the first heat treatment falls between 500xc2x0 C. and 750xc2x0 C., and
the temperature for the second heat treatment falls between 800xc2x0 C. and 1100xc2x0 C.
Still another aspect of the invention is a method for producing a semiconductor device, which comprises;
a step of keeping a material that contains phosphorus and a metal element capable of promoting the crystallization of silicon, in contact with a partial region of an amorphous silicon film,
a step of first heat treatment for diffusing the metal element from said partial region into the amorphous silicon film to thereby attain crystal growth in the film,
a step of second heat treatment for diffusing phosphorus from said partial region into the amorphous silicon film to thereby make the metal element gettered by the thus-diffused phosphorus, and
a step of removing the region into which phosphorus has diffused,
wherein;
the temperature for the first heat treatment falls between 500xc2x0 C. and 750xc2x0 C.,
the temperature for the second heat treatment falls between 800xc2x0 C. and 1100xc2x0 C., and
the diffusion distance for the metal element is longer than that for phosphorus.